In Japan, analog broadcasting will end in 2011. Also in other developed countries, analog broadcasting will end and change to digital broadcasting. Demand for replacement purchases of televisions is thus expected to grow by about 2011 in the developed countries.
After 2012, however, television demand in the developed countries is predicted to slump. In contrast, in developing countries, such as Asia and South America, television demand is expected to grow also after 2012 because of their high economic growth rate. After 2012, the developing countries will play a central role in the television market.
In the developing countries, their broadcasting environments are so poor that video signals transmitted by analog broadcasting are weak in electric field and thus much noisy. Moreover, digital broadcasting in the developing countries often rebroadcasts video signals obtained by digitalizing analog video pictures recorded on a video tape. Such video signals have much noise. A noise reduction technology is thus essential for televisions for the developing countries.
As the noise reduction technology, a low-pass filter is known. Although the low-pass filter can reduce noise, it poses a problem that a video picture blurs.
Liquid crystal televisions now on the market in the developing countries are equipped with a digitalized image processing circuit. Such a liquid crystal television uses thus an adaptive low-pass filter utilizing a digital technology in order to reduce noise. An example of the adaptive low-pass filter is disclosed in Patent Literature 1.
FIGS. 20 through 22 are diagrams illustrating the adaptive low-pass filter disclosed in Patent Literature 1. As illustrated in FIG. 20, in this technology, noise of a target pixel 1 is removed with the use of values of nine pixels including adjacent eight pixels (hereinafter referred to as pixel values). A noise detection circuit 3 detects whether or not each of the nine pixels is noisy. A median filter circuit 2 will replace a pixel value of the pixel detected as noisy with a median of pixel values of the nine pixels. In this context, the median refers to the center value, i.e., the fifth pixel value of the pixel values of the nine pixels arranged in descending order (see FIG. 21).
As illustrated in FIG. 22, the noise detection circuit 3 includes a vertical direction noise detection circuit 5, a horizontal direction noise detection circuit 6, and other members.
The vertical direction noise detection circuit 5 detects differences in pixel value between the target pixel and pixels adjacent upwards and downwards to the target pixel. The vertical direction noise detection circuit 5 defines the target pixel as a vertical noise candidate when both the differences exceed a threshold.
The horizontal direction noise detection circuit 6 detects differences in pixel value between the target pixel and pixels adjacent leftwards and rightwards to the target pixel. The horizontal direction noise detection circuit 6 defines the target pixel as a horizontal noise candidate when both the differences exceed a threshold.
If the target pixel is the vertical noise candidate and the horizontal noise candidate, then the pixel value of the target pixel will be replaced with the median.